Bipyridyl-type Ligands Research Articles

Nickel/Photoredox Dual-Catalyzed Regiodivergent Aminoalkylation of Unactivated Alkyl Halides.

A mild and regiodivergent aminoalkylation of unactivated alkyl halides is disclosed via a dual photoredox/nickel catalysis. Bipyridyl-type ligands without an ortho-substituent control the site-selective coupling at the original position, while ortho-disubstituted ligands tune the site-selectivity at a remote, unprefunctionalized position. Mechanistic studies combined with DFT calculations give insight into the mechanism and the origins of the ligand-controlled regioselectivity. Notably, this redox-neutral, regiodivergent alkyl-alkyl coupling features mild conditions, broad substrate scope for both alkyl coupling partners, and excellent site-selectivity and offers a straightforward way for α-alkylation of tertiary amines to synthesize structurally diverse alkylamines and value-added amino acid derivatives.

Preparation, characterization and luminescence-sensing properties of two ZnII MOFs with mixed 5-amino-2,4,6-tribromoisophthalic acid and bipyridyl-type ligands

The bromo-substituted aromatic dicarboxylic acid 5-amino-2,4,6-tribromoisophthalic acid (H2ATBIP), in the presence of the N-donor flexible bipyridyl-type ligands 1,3-bis(pyridin-4-yl)propane (bpp) and N,N'-bis(pyridin-4-ylmethyl)oxalamide (4-bpme) and ZnII ions, was used as an O-donor ligand to assemble two novel luminescent metal-organic frameworks (MOFs), namely poly[[(μ-5-amino-2,4,6-tribromoisophthalato-κ2O1:O3)[μ-1,3-bis(pyridin-4-yl)propane-κ2N:N']zinc(II)] dimethylformamide monosolvate], {[Zn(C8H2Br3NO4)(C13H14N2)]·C3H7NO}n, (1), and poly[[(μ-5-amino-2,4,6-tribromoisophthalato-κ2O1:O3)diaqua[μ-N,N'-bis(pyridin-4-ylmethyl)oxalamide-κ2N:N']zinc(II)] monohydrate], {[Zn(C8H2Br3NO4)(C14H14N4O2)(H2O)2]·H2O}n, (2), using the solution evaporation method. Both (1) and (2) were characterized by FT-IR spectroscopy, elemental analysis (EA), solid-state diffuse-reflectance UV-Vis spectroscopy, and powder and single-crystal X-ray diffraction analysis. Complex (1) shows a two-dimensional (2D) corrugated layer simplified as a 2D (4,4) topological network. The supramolecular interactions (π-π stacking, hydrogen bonding and C-Br...Br halogen bonding) play significant roles in the formation of an extended three-dimensional (3D) supramolecular network of (1). Complex (2) crystallizes in the chiral space group P212121 and exhibits a novel 3D homochiral framework, showing a diamond-like topology with Schläfli symbol 66. The homochirality of (2) is further confirmed by the solid-state circular dichroism (CD) spectrum. The second harmonic generation (SHG) property of (2) was also investigated. The hydrogen and C-Br...Br/O halogen bonding further stabilize the framework of (2). The central ZnII ions in (1) and (2) show tetrahedral and octahedral coordination geometries, respectively. The coordinated and uncoordinated water molecules in (2) could be removed selectively upon heating. Most importantly, (1) and (2) show rapid and highly sensitive sensing for a large pool of nitroaromatic explosives (NAEs).

Indium Phosphite‐Based Porous Solids Exhibiting Organic Sensing and a Facile Route to Superhydrophobicity

In searching for practical crystalline porous solids, two unique hybrid materials with featured functions, In-bpy and In-dpe, were prepared without deliberately designed organic linker units or complex post-modification procedures. Composed of oxalate-embedded metal phosphite (MPO) sheets and bipyridyl-type ligands of varied molecular lengths, they show a common pillar-layered topology but are the first well-characterized organo-MPOs to possess genuine porosity, substantiated by CO2 adsorption, and structural stability under harsh conditions. In-bpy exhibits a turn-on fluorescence signal when in contact with p-xylene, making it the first MPO-based sensing material with selectivity and recyclability. Furthermore, In-dpe demonstrates a facile and unprecedented route to the superhydrophobicity of porous solids via a [2+2] photocycloaddition reaction between linker and foreign units. Our findings suggest that MPO may serve as a promising platform for hybrid frameworks to create many more functional porous materials.

Perplexing Coordination Behaviour of Potentially Bridging Bipyridyl-Type Ligands in the Coordination Chemistry of Zinc and Cadmium 1,1-Dithiolate Compounds

The X-ray structural chemistry of zinc and cadmium 1,1-dithiolates (for example, xanthate, dithiophosphate and dithiocarbamate) with potentially bridging bipyridyl-type ligands (for example, 4,4′-bipyridine) is reviewed. For zinc, the xanthates and dithiophosphates uniformly form one-dimensional coordination polymers, whereas the zinc dithiocarbamates are always zero-dimensional, reflecting the exceptional chelating ability of dithiocarbamate ligands compared with xanthates and dithiophosphates. For cadmium, one-dimensional coordination polymers are usually found, reflecting the larger size of cadmium compared with zinc, but zero-dimensional aggregates are sometimes found. Steric effects associated with the 1,1-dithiolate-bound R groups are shown to influence supramolecular aggregation and, when formed, polymer topology in order to reduce steric hindrance; the nature of the bipyridyl-type ligand can also be influential. For the dithiocarbamates of both zinc and cadmium, in instances where the dithiocarbamate ligand is functionalised with hydrogen bonding potential, extended supramolecular architectures are often formed via hydrogen bonding interactions. Of particular interest is the observation that the bipyridyl-type ligands do not always bridge zinc or cadmium 1,1-dithiolates, being monodentate instead, often in the presence of hydrogen bonding. Thus, hydroxyl-O–H…N(pyridyl) hydrogen bonds are sometimes formed in preference to M←N(pyridyl) coordinate-bonds, suggesting a competition between the two modes of association.

Photochemical and Photobiological Activity of Ru(II) Homoleptic and Heteroleptic Complexes Containing Methylated Bipyridyl-type Ligands.

Light-activated compounds are powerful tools and potential agents for medical applications, as biological effects can be controlled in space and time. Ruthenium polypyridyl complexes can induce cytotoxic effects through multiple mechanisms, including acting as photosensitizers for singlet oxygen (1O2) production, generating other reactive oxygen species (ROS), releasing biologically active ligands, and creating reactive intermediates that form covalent bonds to biological molecules. A structure-activity relationship (SAR) study was performed on a series of Ru(II) complexes containing isomeric tetramethyl-substituted bipyridyl-type ligands. Three of the ligand systems studied contained strain-inducing methyl groups and created photolabile metal complexes, which can form covalent bonds to biomolecules upon light activation, while the fourth was unstrained and resulted in photostable complexes, which can generate 1O2. The compounds studied included both bis-heteroleptic complexes containing two bipyridine ligands and a third, substituted ligand and tris-homoleptic complexes containing only the substituted ligand. The photophysics, electrochemistry, photochemistry, and photobiology were assessed. Strained heteroleptic complexes were found to be more photoactive and cytotoxic then tris-homoleptic complexes, and bipyridine ligands were superior to bipyrimidine. However, the homoleptic complexes exhibited an enhanced ability to inhibit protein production in live cells. Specific methylation patterns were associated with improved activation with red light, and photolabile complexes were generally more potent cytotoxic agents than the photostable 1O2-generating compounds.

Crystal structures of {μ2-N,N'-bis-[(pyridin-3-yl)meth-yl]ethanedi-amide}tetra-kis-(di-methyl-carbamodi-thio-ato)dizinc(II) di-methyl-formamide disolvate and {μ2-N,N'-bis-[(pyridin-3-yl)meth-yl]ethanedi-amide}tetra-kis-(di-n-propyl-carbamodi-thio-ato)dizinc(II).

The title structures, [Zn2(C3H6NS2)4(C14H14N4O2)]·2C3H7NO (I) and [Zn2(C7H14NS2)4(C14H14N4O2)] (II), each feature a bidentate, bridging bipyridyl-type ligand encompassing a di-amide group. In (I), the binuclear compound is disposed about a centre of inversion, leading to an open conformation, while in (II), the complete mol-ecule is completed by the application of a twofold axis of symmetry so that the bridging ligand has a U-shape. In each of (I) and (II), the di-thio-carbamate ligands are chelating with varying degrees of symmetry, so the zinc atom is within an NS4 set approximating a square-pyramid for (I) and a trigonal-bipyramid for (II). The solvent di-methyl-formaide (DMF) mol-ecules in (I) connect to the bridging ligand via amide-N-H⋯O(DMF) and various amide-, DMF-C-H⋯O(amide, DMF) inter-actions. The resultant three-mol-ecule aggregates assemble into a three-dimensional architecture via C-H⋯π(pyridyl, chelate ring) inter-actions. In (II), undulating tapes sustained by amide-N-H⋯O(amide) hydrogen bonding lead to linear supra-molecular chains with alternating mol-ecules lying to either side of the tape; no further directional inter-actions are noted in the crystal.

Novel and Efficient Chromium(II)-Mediated Desulfonylation of α-Sulfonyl Ketone

A novel and efficient method for the Cr(II)-mediated desulfonylation of α-sulfonyl ketone by a Cr-ligand-Mn system has been developed during the course of process research on Halaven (eribulin mesylate). This reaction is dramatically accelerated in the presence of an appropriate bipyridyl-type ligand. This system is applicable to reduction of α-sulfur-substituted ketones. In addition, a Cr-Cp2ZrCl2-Mn catalytic system is also applicable to desulfonylation of α-sulfonyl ketone.

Controlled Stacking and Unstacking of Peripheral Chlorophyll Units Drives the Spring‐Like Contraction and Expansion of a Semi‐Artificial Helical Polymer

Developing new strategies for controlling polymer conformations through precise molecular recognition can potentially generate a machine-like motion that is dependent on molecular information-an important process for the preparation of new intelligent nanomaterials (e.g., polymer-based nanomachines) in the field bordering between polymer chemistry and conventional supramolecular sciences. Herein, we propose a strategy to endow a helical polymer chain with dynamic spring-like (contraction/expansion) motion through the one-dimensional self-assembly (aggregation/disaggregation) of peripheral amphiphilic molecules. In this developing system, we employed a semi-artificial helical polysaccharide presenting peripheral amphiphilic chlorophyll units as a power device that undergoes contractive motion in aqueous media, driven by strong π-π interactions of its chlorophyll units or by cooperative molecular recognition of bipyridyl-type ligands through pairs of chlorophyll units, thereby converting molecular information into the regulated motion of a spring. In addition, this system also undergoes expansive motion through coordination of pyridine. We anticipate that this strategy will be applicable (when combined with the established wrapping chemistry of the helical polysaccharide) to the development of, for example, drug carriers (e.g., nano-syringes), actuators (stimuli-responsive films), and directional transporters (nano-railways), thereby extending the frontiers of supramolecular science.

Thiodiacetate–Manganese Chemistry with N ligands: Unique Control of the Supramolecular Arrangement over the Metal Coordination Mode

Compounds based on the Mn-tda unit (tda=S(CH(2)COO)(2)(-2) ) and N co-ligands have been analyzed in terms of structural, spectroscopic, magnetic properties and DFT calculations. The precursors [Mn(tda)(H(2)O)](n) (1) and [Mn(tda)(H(2)O)(3)]·H(2)O (2) have been characterized by powder and X-ray diffraction, respectively. Their derivatives with bipyridyl-type ligands have formulas [Mn(tda)(bipy)](n) (3), [{Mn(N-N)}(2)(μ-H(2)O)(μ-tda)(2)](n) (N-N=4,4'-Me(2)bipy (4), 5,5'-Me(2)bipy, (5)) and [Mn(tda){(MeO)(2)bipy}·2H(2)O](n) (6). Depending on the presence/position of substituents at bipy, the supramolecular arrangement can affect the metal coordination type. While all the complexes consist of 1D coordination polymers, only 3 has a copper-acetate core with local trigonal prismatic metal coordination. The presence of substituents in 4-6, together with water co-ligands, reduces the supramolecular interactions and typical octahedral Mn(II) ions are observed. The unicity of 3 is also supported by magnetic studies and by DFT calculations, which confirm that the unusual Mn coordination is a consequence of extended noncovalent interactions (π-π stacking) between bipy ligands. Moreover, 3 is an example of broken paradigm for supramolecular chemistry. In fact, the desired stereochemical properties are achieved by using rigid metal building blocks, whereas in 3 the accumulation of weak noncovalent interactions controls the metal geometry. Other N co-ligands have also been reacted with 1 to give the compounds [Mn(tda)(phen)](2)·6H(2)O (7) (phen=1,10-phenanthroline), [Mn(tda)(terpy)](n) (8) (terpy=2,2':6,2''-terpyridine), [Mn(tda)(pyterpy)](n) (9) (pyterpy=4'-(4-pyridyl)-2,2':6,2''-terpyridine), [Mn(tda)(tpt)(H(2)O)]·2H(2)O (10) and [Mn(tda)(tpt)(H(2)O)](2)·2H(2)O (11) (tpt=2,4,6-tris(2-pyridyl)-1,3,5-triazine). Their identified mono-, bi- or polynuclear structures clearly indicate that hydrogen bonding is variously competitive with π-π stacking.

Relationship between Channel and Sorption Properties in Coordination Polymers with Interdigitated Structures

Porous coordination polymers constructed from Zn(2+) and isophthalate with linear bipyridyl-type ligands were synthesized. [Zn(ip)(bpb)](n) (CID-21; ip=isophthalate, bpb=1,4-bis(4-pyridyl)benzene), [Zn(ip)(bpt)](n) (CID-22; bpt=3,6-bis(4-pyridyl)-1,2,4,5-tetrazine), and [Zn(ip)(bpa)](n) (CID-23; bpa=1,4-bis(4-pyridyl)acetylene) all have interdigitated structures of layers and similar void volumes (≈27%). In these compounds, 1D bottleneck-type channels run along the perpendicular direction of the layer stacking and their properties are strongly dominated by the dipyridyl linker ligands. Because of the difference in packing of 2D layers, CID-21 and CID-22 have relatively rigid porous structures, whereas CID-23 has greater flexibility, as indicated by the results of powder X-ray diffraction studies. The micropores of CID-22 surrounded by tetrazine moieties adsorb polar molecules, such as methanol and water. The higher affinity of CID-22 for water than CID-21 is supported by a theoretical study. The 1D channel of CID-23 is wider than that of the other two compounds, which enables the incorporation of aromatic molecules. This is because the shape of the bpa linker ligand generates a wider pore diameter (8.6 Å). Only CID-23 can adsorb a benzene molecule and the isotherm of benzene has a gate-opening-type profile. This offers proof of the guest accommodation process through large structural transformation from a nonporous to a porous structure. The flexibility and restricted pore space of CID-23, at 298 K, allows only benzene, but not cyclohexane, to enter the channels. The porous structure exhibits clear selectivity for these similar guests. The incorporation of an elongated dipyridyl linker ligand in the 2D coordination layers provides a strategy for the design of microporous compounds with different flexibilities, microporous environments, and separation abilities.

1,4-Bis(3-pyridylmethyleneaminomethyl)benzene

The title compound, C20H18N4, is a flexible 3,3′-bipyridyl-type ligand with a long spacer group between the two pyridyl functions. The mol­ecule crystallizes around an inversion center, with one half-mol­ecule in the asymmetric unit and a dihedral angle of 71.85 (8)° between the pyridine ring and the central benzene ring.

{μ-N,N′-Bis[(E)-4-pyridylmethylidene]naphthalene-1,5-diamine}bis[dichlorido(dimethyl sulfide)platinum(II)

The title dinuclear platinum compound, [Pt2Cl4(C22H16N4)(C2H6S)2], with a long bridging bipyridyl-type ligand, is centrosymmetric and the PtII cation shows a slightly distorted square-planar coordination geometry. The Cl ligands are trans to each other, with a Cl—Pt—Cl angle of 178.83 (8)°. The pyridine ring forms a dihedral angle of 48.8 (2)° with the planar PtCl2SN unit. Within the mol­ecule, the distance between Pt atoms is 20.262 (5) Å and the N⋯N separation between the terminal pyridyl rings is 16.23 (1)Å.

Cadmium coordination polymers with different topologies depending on preparation methods: [Cd L1.5(NO 3) 2], [Cd L2(NO 3) 2] · (C 6H 6), and [Cd L2(NO 3) 2] · 2(C 4H 8O) ( L = 3-py–CH [dbnd]N–(CH 3)C 6H 3–C 6H 3(CH 3)–N [dbnd]CH–3-py)

Novel cadmium coordination polymers [Cd L 1.5(NO 3) 2] ( 1), [Cd L 2(NO 3) 2] · (C 6H 6) ( 2), and [Cd L 2(NO 3) 2] · 2(C 4H 8O) ( 3), which contain a common long 3,3′-bipyridyl-type ligand, were prepared from Cd(NO 3) 2 · 4H 2O and ligand L (3-py–CH N–(CH 3)C 6H 3– C 6H 3(CH 3)–N CH–3-py). Whereas polymer 1 was prepared by solvothermal reactions, polymers 2 and 3 were prepared by layer diffusion. All have a repeating 84-membered ring unit. Polymer 1 has a non-interpenetrated 1-D ladder structure, and polymers 2 and 3 have a 2-D brick-wall structure. In particular, polymers 2 and 3 contain guest molecules (benzene ( 2) or THF ( 3)) in their frameworks, and the desorption–resorption behavior of the guest molecules is rather reversible.

Long bipyridyl-type linking ligands containing an intervening cyclohexyl fragment and their cadmium coordination polymers: [formula omitted] and [formula omitted] ( Ln = ( n-py)–CH [dbnd]N–C 6H 10–N [dbnd]CH–( n-py); n = 4, 3, 2)

We prepared three isomeric bipyridyl-type ligands ( L n = ( n-py)–CH N–C 6H 10–N CH–( n-py); n = 2–4). Two cadmium coordination polymers, [ Cd L 1.5 4 ( NO 3 ) 2 ] · ( CH 2 Cl 2 ) ( 1) and [ Cd L 1.5 3 ( NO 3 ) 2 ] ( 2), were prepared from cadmium nitrate and ligands L 4 and L 3, respectively. The N⋯N separations between the two terminal pyridyl groups in the free ligands L 4, L 3, and L 2 are 15.798(6), 15.036(4), and 12.417(5) Å, respectively. The 2-D α-arsenic-type polymer 1, which contains CH 2Cl 2 guest molecules, has two distinct N⋯N separations of 15.706(10) Å and 14.479(9) Å and a large 102-membered cyclohexane-like ring unit. The 1-D stair-like polymer 2 has also two distinct N⋯N separations and a 60-membered ring unit. The various lengths of the observed N⋯N separations are due to the ring flip of the intervening cyclohexyl fragment in the ligands.

Novel dienone-based ligands for the synthesis of coordination polymers

New angular exo-dentate 3,3′-bipyridyl-type ligand [L = 2,6-di(3-pyridylmethylidene)cyclohexanone, 1] with conjugated dienone system was used for the synthesis of {[AgL]NO3}n, 2. An X-ray structural determination showed that 2 is composed of polymeric chains (–Ag–L–)n, twinned via metallophilic and stacking interaction.

Stereoselective association of binuclear metallacycles in coordination polymers.

A series of structurally related binuclear metallacycles [Cd(NO(3))(2)L](2), where L is an angular exo-bidentate ligand, have been synthesized. Each metallacycle contains two coordinatively unsaturated, chiral metal centers within a single molecule, and the assembly of these metallacycles into polymeric framework structures has been studied systematically for the first time. Stereoselective homochiral association of [Cd(NO(3))(2)L](2) leads to the formation of helical coordination polymers, whereas meso type association results in nonhelical chain structures. The type of stereoselective aggregation depends on the conditions of self-assembly as well as on ligand functionality. Both helical and nonhelical polymeric complexes have been isolated for the metallacycle [Cd(NO(3))(2)(2,4'-pyacph)](2) (2,4'-pyacph = 2,4'-(4-ethynylphenyl)bipyridyl). Homochiral association results in the formation of helical [Cd(NO(3))]( infinity ) chains which link the binuclear [Cd(NO(3))(2)(2,4'-pyacph)](2) metallacycles into racemic two-dimensional sheets which contain both P and M [Cd(NO(3))]( infinity ) helices. In contrast, meso-association leads to the formation of nonhelical one-dimensional chains. It is shown that the product of homochiral association is predominately formed at room temperature and that of meso-association is generated at elevated temperatures. Thus, it may be concluded that the homochiral association appears to be energetically less favorable than the meso-association, a conclusion that has been confirmed by theoretical calculations of the crystal lattice energy. Several high-yield syntheses of bipyridyl-type ligands used for metallacyclic assembly are also reported.

N,N′-Bis[1-(4-pyridyl)ethylidene]-p-phenylenediamine

The title compound, C20H18N4, is a 4,4′-bipyridyl-type ligand with a long spacer moiety between the two pyridyl functions. Its low-temperature single-crystal analysis reveals that it lies on an inversion center, which is at the center of the 1,4-disubstituted benzene ring.

Pairing of propellers: dimerization of octahedral ruthenium(II) and osmium(II) complexes of eilatin via pi-pi stacking featuring heterochiral recognition.

Five octahedral eilatin complexes of the type [M(L-L)(2)(eilatin)](2+) (M = Ru, Os; L-L = bipyridyl-type ligands) were synthesized, and their dimerization via pi-pi stacking was studied by crystallography and (1)H NMR techniques. The X-ray structures of these racemic complexes were solved and revealed that the eilatin complexes are organized as discrete dimers in which the eilatin residues of each complex are stacked in centrosymmetric packing. Chemical shift dependence on concentration in the (1)H NMR spectra support fast dimer-monomer equilibrium, and the structures of the dimers in acetonitrile solution are proposed to be analogous to their solid-state structures. Dimerization constants in acetonitrile were measured for the five racemic eilatin complexes that exhibit different structural parameters, as well as for the two enantiomeric forms of one of these complexes. They were found to be independent of the metal (Ru vs Os), strongly dependent on the steric effects introduced by the L-L ligands (2,2'-bipyridine, 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, and 2,2'-biquinoline), and dependent on the optical purity of the complexes. A clear preference for heterochiral over homochiral dimer formation was demonstrated. This is the first report of chiral recognition in solution, exhibited by simple chemical systems held solely by pi-stacking interactions.

Supramolecular porphyrin-based materials. Assembly modes of [5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrinato]zinc with bipyridyl ligands

Reaction of [5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrinato]zinc with bipyridyl-type ligands leads to the formation of extended three-dimensional supramolecular architectures sustained by a concerted mechanism of metal–ligand (pyridyl-N⋯Zn) coordination and cooperative intermolecular (O–H⋯OH and O–H⋯N) hydrogen bonding. The competing nature of these interactions, along with the different length and functionality of the ligand auxiliaries, affects the resulting motifs of the porphyrin–ligand supramolecular assembly. Herein we describe new heterogeneous complexes of this type, and evaluate the various modes of intermolecular association in these materials.

Synthesis of New Chiral 2,2‘-Bipyridyl-Type Ligands, Their Coordination to Molybdenum(0), Copper(II), and Palladium(II), and Application in Asymmetric Allylic Substitution, Allylic Oxidation, and Cyclopropanation

A series of chiral bipyridine-type ligands 5−12 has been synthesized via a de novo construction of the pyridine nucleus. The chiral moieties of the ligands originate from the monoterpene realm, namely, pinocarvone (13 → 6, 7, and 9), myrtenal (18 → 5), nopinone (21 → 8 and 10), and menthone (28 → 11 and 12); the first three precursors can be obtained in one step from β- and α-pinene, respectively. Complexes of these ligands with molybdenum(0) (38−40) and copper(II) (41) have been characterized by single-crystal X-ray crystallography. While complex 38 exhibits polymorphism (monoclinic and tetragonal forms crystallize from the same batch), 41 is characterized by a tetrahedrally distorted geometry of the metal coordination. The Mo and Pd complexes exhibit modest asymmetric induction in allylic substitution (43 → 44), and the Cu(I) counterpart of 41, derived from 10 (PINDY) and Cu(OTf)2, shows promising enantioselectivity (49−75% ee) and reaction rate (≥30 min at room temperature) in allylic oxidation of cyclic olefins (47 → 48). The Cu(I) complex of 11 (MINDY) proved effective in cyclopropanation (49 → 50) with up to 72% ee.